Magnetic Resonance Imaging (MRI) technology has been more and more widely used in modern medical diagnosis due to its advantages of no radiation, high resolution imaging for soft tissue and developing for brain function. However, nowadays, the risk of radio frequency (RF) heating makes the patients implanted with medical apparatus such as a nerve stimulator or pacemaker, etc. unable to conduct a MRI inspection in high field intensity. The FDA reported a case in which a Parkinson patient implanted with a deep brain stimulator conducted a MRI inspection which caused him in a coma and permanently disabled. This issue makes many patients have a lot of restrictions when they needed to conduct a MRI inspection.
The research shows that, heating mainly occurs at the tip of the metallic implant. For example, for a deep brain stimulator, heating mainly occurs around the contact of the electrode. This is because metal contact will produce turbulence in a RF field of MRI on one hand; and on the other hand, as the electrode acting as an antenna in the RF field, the electric field induced on the electrode will cause heating at the contact.
The heating effect is related to the position and shape of the electrode in a MRI magnetic field. In some specific positions and shapes, the electrode can avoid resonance of a MRI magnetic field so as to avoid over-heating. However, in practical applications, the implanting manner of electrodes in a human body cannot be undetermined, and therefore it is necessary for the electrode itself to meet safety requirement under a resonance condition.